Gold hit a three-week high Tuesday and has since pulled back as stocks have risen, but the real story this week has been silver.

After breaking through the psychologically key $16 level, the white metal hit a fresh 5.5-month high of $16.31 and is now up more than 15% for the year.

Silver is finally catching up to the gold rally, Bloomberg noted Tuesday. Silver rallied 7.8% in the past four sessions, more than twice the pace of golds increase, helped by signs of improving industrial demand and mounting speculation that the Federal Reserve will be slow to boost interest rates.

ETFs go through the roof: One reason for silvers resurgence has been strong inflows into exchange-traded funds linked to the metal, while in contrast, gold ETF holdings have been relatively flat in recent weeks. According to Bloomberg, silver ETF holdings have jumped to December 2014 highs.

With about 946 metric tons of silver added to ETFs this year, silver holdings of physically backed ETFs have gone through the roof, Natixis analyst Bernard Dahdah told Reuters.

Eagle sales at record clip: Investments in physical silver also are soaring. As of Tuesday, sales totals of silver American Eagle bullion coins have hit 15.964 million ounces. Thats 31.2% higher than sales at the same time in 2016, which was a record year for silver Eagles.

Meanwhile, the Perth Mint was reporting its strongest silver sales in six months, with the Australian company logging its seventh straight month of sales above 1 million ounces. Its March silver bullion sales are 67.4% higher than Februarys and 175% higher than March 2015.

Maple Leaf sales up 76%: Moreover, according to Jason Hamlin of GoldStockBull, in Canada, the latest quarterly report of Silver Maple Leafs had sales up 76% year on year. Indian silver imports were a record 8,506 tonnes (273,473,854 ounces) in 2015.

Hamlins conclusion? The bottom line is that silver is in the early stage of confirming golds bullish breakout in 2016. It now just needs to push above $16 and hold this level for a few consecutive days.

Key ratio favors silver: The widely watched gold-silver ratio also is flashing a buy signal for the white metal. Down from its March peak of 83.2, its now near 78.7, meaning that it takes that many ounces of silver to buy a single ounce of gold. Though now at about 3.5-month lows, the current ratio still continues to suggest that silver is very undervalued relative to gold.

We see further potential for the silver price to catch up on the gold price in the medium term, Commerzbank analysts wrote. That said, the silver price could suffer a setback in the short term as we believe that it has risen too quickly especially given that speculative financial investors continued to bet heavily on climbing silver prices in the week to April 5, with net long positions totaling 43,300 contracts.